Reactance tube circuit



June 12, 1951 R. E. MOE 2,556,883

REACTANCE-TUBE CIRCUIT Filed Feb. 25, 1 948 Inventor: Robert E. Moe,

byW-ZDM H is Atto'rhey.

Patented June 12, 1951 York 2,556,883 UNITED STATES PATENT OFFICEREACTANCE TUBE CIRCUIT Robert E. Moe, Syracuse, N. i'r assigncr'toGeneral Electric Company, a corporation of New Application February 25,1948, Serial No. 10,773 s Claims. (01. 250-36) sible to reverse thepositions or R and C and change their values and thus achieve a 90'degree phase shift in the opposite direction, but the residualcomponent is still degenerative. An inductance may be inserted'in thiscircuit to give the desired 90 degree phase shift, but this combinationis frequency-sensitive and is not applicable over a wide band offrequencies.

It is an object of my invention to provide a reactance tube circuit thathas 'a negative-resistance residual component.

Another object of my invention is to provide a reactance tube circuitthat aids the oscillator rather than loading it.

Afu'rther object of my invention is toprovide a reactance tube circuitthat'is efiective throughout a wide range o'f frequenci'es.

The features of my invention which I believeto be novel are set forthwith .particularity in the appended claims. My invention itself,however, together with further objects and advantages thereof may bestbe understood by reference to the following description taken inconjunction with the accompanying drawing in which Fig. 1 is a schematicdiagram of a typical reactance tube circuit; and Fig. 2 is a schematicdiagram of a reactance tube circuit embodying my invention.

Referring now to Fig. 1, I have shown a reactance tube circuit using apentode discharge device I having an anode 2, a cathode :3, a grid 4, agrid and a grid 6. The cathode 3 is connected to ground and the grid 6is connected to the cathode 3. The anode voltage is supplied from asuitable B+ supply represented conventionally by bus I8, through a radiofrequency choke I-I A unidirectional control voltage for grid 4 issupplied from a suitable control source (not shown) through a resistor9. The grid 5 is supplied from the 13+ supply by a resistor l2 "and is'by-passed to ground through a capacitor [3.

The output of an oscillator: 15, having a tuned circuit comprising acapacitor 4 6 and inductance I1, is connected, through a couplingcapacitor 14 and blocking capacitor l0, across the phase shiftingnetwork'comprising the resistance] and the capacitor 8. The commonterminal of the capacitors'and the resistor 1 is connected to the grid'4. The oscillator [5 may be any suitable self-excited oscillator ofwhich various types are i choke 28. Control grid 26 is connected toground.

well known to those skilled in the "art. "If'the re- -sistance 1 is, forexample, ten times the impedance of the capacitance 8, the phase shiftof of the resultant voltage on the grid 4 of the reactance tube l is84.3 degrees (lagging) from the voltage across the tuned circuit. Thiscauses a similar current to flow in the anode circuit which is alsoacross the tuned circuit. Thus,

where I1) is the anode current, gm is mutual conductance, X0 is thecapacitive reactance, and E1; is the anode voltage. The effectiveimpedance Z is then Now the 45,000 ohm term represents an equivalentinductive reactance across the circuit, in "series with a 500-ohm pureresistance. This is a result of the incomplete phase shift of the RCcircuit. This effect can be reduced by making R in which case the phaseshift will be 89.4 degrees and Z=500+i50,000 ohms (4) In the lattercase, however, the reactance effect "is reduced and will be equivalentto the impedance of 3 micromicrofarads at 1,000 kilocycles. The "effectof the additional resistance is to 'load the tuned circuit of theoscillator, in addition to the shunt effect of the phase shift networkRC, so that the amplitude of the oscillator varies markedly with thevalue of the unidirectional control voltage applied to the grid l of thereactance tube I through the resistor 9 which is high in comparison tothe resistor 1. Actually, in most instances with this arrangement, it isnot possible to obtain the desired amount of frequency shift before theoscillator stops oscillating completely. 7

Referring now to Fig. 2, I have shown a reactance tube circuit embodyingthe invention which comprises a discharge device 20 which, forillustration, I have shown as a double triode such as a commercial type6J6. One section 20a has a cathode'ZZ, control grid 23 and anode 24 andthe other section 201) has a cathode'25, control grid 3'6and anode 21.The oscillator I5 is represented asfthe same type as in Fig. 1. Theupper end of inductance H is connected to the anode 21 through acoupling capacitor 2 I.

Anod'e potential is supplied-from the B+ supply bus 18 to anode 21through'aradio frequency The cathodes 22 and 25 are tied together andare connected to ground through a radio frequency choke 29. The anode 24is connected directly to the 13+ supply. The phase shift network,comprising resistance 1 and capacitance 8, is the same as in Fig. 1. Thecontrol grid 23 is also again connected to a suitable source ofunidirectional control voltage through resistor 9.

Essentially, the reactance circuit of Fig. 2 comprises acathode-follower section 20a, driving a grounded-grid amplifier section201), such that an increase in voltage on grid 23 produces a decrease inplate current at plate 21.

Is can be seen from the above description of Fig. 2 that the anodecurrent through the anode 21 is 180 degrees out of phase with thevoltage at the grid 23. Assuming the effective plate load m to be 50,000ohms and the reactance device 20 to be a type 6J6 with a a of 35 and aplate resistance r of 7,000 ohms for each section, then- Thus, it may beseen that this circuit introduces a negative resistance in series withan equivalent capacitance across the tuned circuit of the oscillator,which compensates for the losses in the resistor 1 that shunts the tunedcircuit. In other words, it aids the oscillator rather than loading itdown. I The control voltage on the grid 23 can, therefore, be variedover a much wider range without any appreciable change in the amplitudeof oscillations.

It should be understood by those skilled in the art that the inventionis not limited to a doubletriode circuit, which is shown merely forpurposes of illustration. A pentode might be used for the section 201)which would increase the control effect because of the higher gain thatcould be realized due to its higher plate resistance.

While a specific embodiment of my invention has been shown and describedand certain modifications suggested, it will, of course, be understoodthat various other modifications may be made without departing from theinvention. The appended claims are, therefore, intended to cover anysuch modifications within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A reactance circuit comprising first and second electron dischargedevices each including an anode, a cathode and a control electrode, saiddevices having their cathodes connected to a common reference pointthrough a common cathode load impedance so that a voltage applied to thecontrol electrode of said first device produces an anode current changein said second device 180 electrical degrees out of phase therewith,means for impressing an alternating voltage between the anode of saidsecond device and said point, and means comprising a phase shift networkinterconnecting the anode of said second device with the controlelectrode of said first device for feeding said voltage between thecontrol electrode of said first device and said point, said networkproducing a voltage phase shift of less than 90 electrical degrees inthe voltage impressed on the grid of said first device,

thereby to cause the effective impedance at the anode of said seconddevice to consist of a reactive component and a negative resistancecomponent.

2. A variable reactance circuit comprising first and second electrondischarge devices each including an anode, a cathode and a control grid,said devices being coupled together through a common cathode impedance,said second device also having a separate load impedance connected toits anode, whereby a voltage variation at the grid of said first deviceproduces an in-phase voltage variation at the anode of said seconddevice, means for impressing an alternating voltage on said anode ofsaid second device, means comprising an alternating-currentphase-shiftin network connected across said second device and saidcathode impedance in series, said network having an intermediate pointthereon at which a corresponding alternating voltage appears with aphase shift of less than electrical degrees, with respect to said firstvoltage, a connection from said intermediate point to the grid of saidfirst device, thereby to produce a correspondingly phase-shifted voltageacross said cathode impedance and to cause the effective impedanceacross the anode of said second device and said cathode impedance inseries to consist of a reactive component and a negative resistancecomponent, and means to vary said second impedance comprising a sourceof control voltage connected to the grid of said first device.

3, A variable reactance circuit for controlling the frequency of a, highfrequency oscillatory system, comprising first and second electrondischarge devices each having a cathode, an anode, and a control grid,said devices being coupled together through a common cathode impedanceconnected from their cathodes to a reference point, means connectingsaid anodes to said point through sources of anode operating potential,said second device also having a separate anode load impedance andhaving its grid connected directly to said point, means for impressinghigh frequency voltages from said oscillatory system between the anodeof said second device and said point, means for impressin low frequencyand unidirectional control potentials between the grid of said firstdevice and said point, a phase shifting network connected from the anodeof said second device to said point comprising a resistive and areactive element in series, and a connection from the grid of said firstdevice to a point on said network located between said resistive andreactive elements and at which high frequency voltage appears with aphase shift of somewhat less than 90 electrical degrees, whereby theeffective impedance connected across the system has a negativeresistance component as well as a reactive component.

ROBERT E. MOE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,140,339 Travis Dec. 31, 19382,181,909 Peterson Dec. 5, 1939 2,248,132 Smith July 8, 1941 2,253,470Rath Oct. 7, 1941 2,441,504 OBrien May 11, 1948 2,469,194 Delvaux May 3,1949

